TRANSACTIONS OF SECTION H. 785 



Every nerve-cell, with the nerve axial fibre arising from and belonging to it, 

 is now called a Neurone, and both brain and spinal cord are built up of tens of 

 thousands of such neurones. It may reasonably be assumed that the larger the 

 brain the more numerous are the neurones which enter into its constitution. The 

 greater the number of the neurones, and the more complete the connections which 

 the several areas have with each other through their axial fibres, the more complex 

 becomes the internal mechanism, and the more perfect the structure of the organ. 

 We may reasonably assume that this perfection of structure finds its highest 

 manifestations in the brain of civilised men. 



The specialisation in the relations and connections of the axial fibre processes 

 of the neurones, at their termination in particular localities, obviously points to 

 functional differences in the cortical and other areas, to which these processes 

 extend. It has now been experimentally demonstrated that the cortex of the 

 cerebrum is not, as M. Flourens conceived, of the same physiological value 

 throughout ; but that particiUar functions are localised in definite areas and con- 

 volutions. In speaking of localisation of function in the cerebrum, one must not 

 be understood as adopting the theory of Gall, that the mental faculties were 

 definite in their number, that each had its seat in a particular region of the 

 cortex, and that the locus of this region was marked on the surface of the skull 

 and head by a more or less prominent ' bump.' 



The foundation of a scientific basis for localisation dates from 1870, when 

 Fritsch and Hitzig announced that definite movements followed the application of 

 electrical stimulation to definite areas of the cortex in dogs. The indication thus 

 given was at once seized upon by Uavid Ferrier, who explored not only the hemi- 

 spheres of dogs, but those of monkeys and other vertebrates.' By his researches 

 and those of many subsequent inquirers, of whom amongst our own countrymen 

 we may especially name Beevor, Horsley, and Schafer, it has now been esta- 

 blished that, when the convolutions bounding, and in close proximity to the fissure 

 of Eolando are stimulated, motor reactions in the limbs, trunk, head and face 

 follow, which have a definite purposive character, corresponding with the volitional 

 movements of the animal. The Rolandic region is therefore regarded as a part of 

 the motor apparatus ; it is called the motor area, and the function of exciting 

 voluntary movements is localised in its cortical grey matter. 



By the researches of the same and other inquirers it has been determined that 

 certain other convolutions are related to the different forms of sensibility, and are 

 sensory or perceptiA'e centres, localised for sight, hearing, taste, smell, and touch. 



Most important observations on the paths of conduction of sensory impressions 

 in the cortex of the convolutions were announced last year by Dr. Flechsig,* of 

 Leipzig, so well known by his researches on the development of the tracts of 

 nerve-fibres in the columns of the spinal cord, published several years ago. He 

 discovered that the nerve-fibres in the cord did not become myelinated, i.e. attain 

 their perfect structure, at a uniform period of time, so that some acquired their 

 complete functional importance before others. He has now applied the same 

 method of research to the study of the development of the human brain, and has 

 shown that in it also there is a difference in the time of attaining perfect structural 

 development of the nerve-tracts. Further, he has discovered that the nerve-fibres 

 in the cerebrum become myelinated, subsequent to the fibres of the other divisions of 

 the cerebro-spinal nervous axis. When a child is born, very few of the fibres of its 

 cerebrum are myelinated, and we have now an anatomical explanation of the 

 reason why an infant has so inactive a brain and is so helpless a creature. It will 

 therefore be of especial interest to determine, whether in those animals which are 

 active as soon as they are born, and which can at once assume the characteristic 

 attitude of the species, the fibres of the cerebrum are completely developed 

 at the time of birth. Flechsig has also shown that the sensory paths myeli- 

 nate before the motor tracts ; that the paths of transmission of touch, and 

 the other impulses conducted by the dorsal roots of the spinal nerves, are 



' West Riding Agijlum lieports, 1873. 



'' Die Localisation der Geistigen Vorgcingc, Leipzig, 1896. 



1897. 3 K 



